Thread: nfa fire flow

  1. #1
    chuck cooke Guest

    Post nfa fire flow


  2. #2
    Phred Guest


    I think the formula you want is:
    (Length x Width)/3 for an "average" occupancy 1 story (10-12 ft) high.

  3. #3
    benson911 Guest


    For Oxygen controlled fires (not vented) use the Volume/100 formula. LxWxH/100

    For non-Oxygen controlled fires (vented) use the Area/3 formula. LxW/3

    Either way, for fire scenes use the thumb up/thumb down for more/less pressure/volume.

    Formulas are for preplanning!

  4. #4
    Joseph Mowery Guest


    If I remember my rural water supply correctly. It's ((len x wid)/3) x (number
    of stories) x % involved = gpm required
    for 3 min flow to control.

  5. #5
    FIRE549 Guest


    The NFA quick-calculation formula is:
    L x W/3 = fire flow for one floor at 100% involvement. Then as you determine the % of involvement upon arrival you can adjust what is needed at that point. For example if 100% involvement of the structure needs 1000 gpm then if the structure is 25% involved you would need 250 gpm. Or if two floors were 100% involved then it would be 2000 gpm.

    In fire-resistive buildings(no unprotected openings)if the floors are not yet involved but are threatened by possible extension of the fire (up to four floors above the fire floor), they should be considered an exposure and 25% of the required fire flow for the fire floor should be added for exposure protection. In all other building construction classes the floors above the fire should be included as part of the fire problem (up to four floors).

    If an adjacent structure is being exposed to fire from the original fire building, 25% of the required fire flow of the building should be added for each side of the fire building with exposures. Should the exposure actually become involved with fire, the exposure(s) then should be treated as a separate fire.

  6. #6
    BIG PAULIE Guest


    This stuff sure sounds pretty tough to do at 2 am when the whole world is on fire. I don't think formulas are for the fireground. Instead why not hit the fire with every thing you got . If this is an over kill then the only thing that will happen is the fire will go out faster.

  7. #7
    Joseph Mowery Guest


    Of course, this would be used for pre-planning. The 3am rule is in effect for the site that you don't have a pre-plan for. Room & contents 1 3/4 w/low pressure nozzle. More fire = more water. Nothing wrong in hitting it hard with a 2 1/2 if you feel the desire or have that gut feeling that there are more to this than what the initial size up gave.

    Stay low, be alert, watch your back.

  8. #8
    Dalmation90 Guest


    I don't know, it is nice to have some idea what kind of fire you can put out. Kinda looks bad if you blow your load on the main fire, discover it wasn't enough and now don't have the water to protect exposures...

    Also nice to do some rough figures at 3am to figure out how many tankers to call, or it's worth laying a very long LDH line.

  9. #9
    benson911 Guest


    Matt, at 3am you can read your preplan with the figuring already done and all you need to do is apply the % involvement to determine the fire flow needed. I think that's the preplanning vs on-scene point we're trying to make.

  10. #10
    Joseph Mowery Guest



    As for the LDH lay, If we have a confirmed structure fire, the 4" hits the ground at the
    best place to establish a drop site. We don't have many hydrants here. Not uncommon to lay all 1200' of 4" and all 600' of 3".

    As for the tankers, all residential fires get three tankers on initial dispatch, three more on second alarm. This also includes 2 engine companies (2 engines each) and a squad on the initial call.

    Commercial building get three engine companies (2 engines), a squad, a ladder, and five tankers on initial alarm and three more tankers on second alarm.

    It helps to have a good initial dispatch in a rural setting. Long response time and its good to start them early than wait until you get on scene and have to start screaming for water.

    Sargent 1

    Stay low, Stay alert, Watch your back.

  11. #11
    Dalmation90 Guest


    Preplans are always also need to have an idea if you have enough water instead of blindly hitting it with all you got and finding out it wasn't enough, and now you don't have enough water to hold the exposures. Probably not a problem for your average house, or garage. Much more important consideration if you have a large agricultural or commercial building going with exposures (both inside and outside).

  12. #12
    benson911 Guest


    I'd like to emphasize Matt's last point. You MUST KNOW how much WATER you have available BEFORE beginning your operation. You may not have enough to put the fire out, but you may have enough to avoid a conflagration.

    Size-Up Size-Up Size-Up

    Consider EVERYTHING you can before you put yourself in an untenable situation.

  13. #13
    e33 Guest


    if the question is how many tankers to call..u preplan certain target hazards for flow and set the tankers on a predetermined automatic aid assignment

    123 main st is a 75 x 100 and requires a 2500gpm fire flow.(according to the above listed formula).

    Box 1 is for 123 main st, since it is a target hazard it has its own box.
    assigned to box 1 are engines 1,2,3 / Truck 1, truck 2/ rescue 1, tanker 1,2,3,4, Chief 1

    this initial assignment can be handle the flow needed for this size building and if engine 1 gets there and upgrades the box to a WF, you fill out an additional few units on the box..tankers engines or whatever

    i agree that calculating fire flows at 3am is nutts, do it before hand and like Paul says just hit fire with water till u knock it down. Its not rocket science. Put more water on the fire to meet and exceed its energy output.

    The opinions and views expressed herin are solely mine and not on the behalf of any department or organization I belong to.

  14. #14
    LHS Guest


    Don't forget the NFA formula is not based upon fact or scientific evidence. It is based upon a survey of NFA students.

  15. #15
    SFDchief Guest


    My theory of when a fire is beyond the pre-planning stages:
    BIG fire, Big hose.
    Works quite well.

  16. #16

    Join Date
    Apr 2008

    Default Wait a minute

    I know this about 8 years too late, but I stumbled upon your forum here and noticed some errors. It is a common misconception that the NFA fire flow formula is lxw/3 for 100% involvement. This is not correct. There are several parameters that go with the formula. The correct formula is lxw/3 for the size of the FIRE, not the size of the room. The formula was only designed for 50% involvement. Any more than 50% involvement, the formula degrades and is not accurate. In addition to this, the formula is for a non-accelerated fire (ordinary fire growth) with ordinary combustibles. This also means you need to be hitting the base of the fire. If you are doing all of this, your fire should go out within 1-2 min. So, if your pre-connect flows 200gpm, you should be able to put out 600 sq ft of ordinary combustibles, in a structure with less than 50% involvement in less than 2 min(Usually less than a minute). If you can't, you might not be hitting the base, or could be dealing with an accelerated fire.
    Some of the things others were saying about just putting a lot of water on it are careless in my opinion. When too much water is applied, this can disrupt the thermal balance, and destroy the survivable space on the ground where victims could be. An ordinary fire that has not had water applied on it has a lot dryer heat that victims can withstand a higher temp. When too much water is put on a fire, the dry heat turns into wet heat and humans can stand wet heat as much (110 degrees in Vegas is easier to deal with than 110 degrees in Baltimore because of the humidity or wet heat). Also, be very conservative with your water. If you are fighing a 100 sq ft fire, you won't need all of your 200 gpm. You only need about 30 gpm, so just use small one second bursts of water and you will be amazed at how well the thermal balance will stay in tact, you will stay cool, and visibility will be great so you can have a much more effective search. If you have doubts about this formula, you could look at the NFA book and find what I just described. I hope this helps you.

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